The present invention relates generally to an imaging optical system, and more particularly to an imaging optical system using a decentered reflecting prism.
Various imaging optical systems including decentered reflecting prisms have been proposed so far in the art. Typically, patent publication 1 has come up with an imaging optical system wherein an aperture stop is provided on both its sides with decentered reflecting prisms, each having a rotationally asymmetric reflecting surface.
On the other hand, patent publication 2 has put forward a ghost light-preventive imaging optical system using a reflecting prism, wherein the reflecting surface of the reflecting prism is provided with a film in its effective area alone, and roughened at its peripheral, non-effective area.
Patent publications 3 and 4 show an image display using a reflecting prism equipped with means for prevention of ghost light resulting from illumination light for a liquid crystal display device.
Patent Publication 1
JP(A)2003-84200
Patent Publication 2
JP(A)9-90229
Patent Publication 3
JP(A)2001-174747
Patent Publication 4
JP(A)2002-118799
In this conjunction, the imaging optical system of patent publication 1 is susceptible of ghost light that is light arriving at an image plane by way of optical paths other than a normal one. On the other hand, patent publications 2, 3 and 4 disclose how to prevent ghost light. With patent publication 2, however, prevention of ghost light is still less than satisfactory. The ghost light referred to in patent publications 3 and 4 is different from that in the case of an imaging optical system, because of stemming from an illumination optical system.
In view of such problems with the prior art as described above, the primary object of the invention is to provide an imaging optical system with reduced or substantially eliminated ghost light.